1. Field of the Invention
The present invention generally relates to motional feedback (MFB) speaker systems and, more particularly, to a MFB speaker system in which the vibration characteristic of a speaker can be arbitrarily controlled and distortion is decreased.
2. Description of the Related Art
FIG. 1 shows a related-art MFB speaker system disclosed in xe2x80x9cSpeaker System (in 2 volumes)xe2x80x9d (Takeo Yamamoto, Radio Technology Publishing, Jul. 15, 1977, p. 406). Referring to FIG. 1, numeral 100 indicates an input terminal of an acoustic signal, 110 indicates an amplifier having a gain of GA, 120 indicates a feedback circuit having a gain of xcex2, and 130 indicates a speaker having a voltage gain of Gs. Ei indicates an input voltage at the terminal 100, Ev indicates an input voltage supplied to the speaker 130 and Es indicates an output voltage from the speaker 130.
A description will now given of the operation.
The acoustic signal input via the input terminal 100 is amplified by the amplifier 110 and drives the speaker 130. The speaker 130 radiates sound as a result of vibration of a diaphragm. The vibration of the diaphragm is detected by a signal detecting means (not shown) provided in the speaker 130 and delivered to the feedback circuit 120. The signal thus fed back is synthesized with the acoustic signal from the input terminal 100 so as to drive the speaker 130.
In this MFB speaker system, the amplifier 110 is used to drive the speaker 130. The amplifier 110 operates in association with the feedback circuit 120 and the speaker 130 so that the entire speaker system operates as a whole. Therefore, it is not generally assumed that a user arbitrarily exchanges the amplifier 110. In the related-art MFB speaker system, the signal returned to the feedback circuit 120 has a negative polarity with respect to the input acoustic signal. Distortion is decreased and the characteristic is improved as a result of the negative feedback.
In the related-art MFB system, the signal detected by the signal detecting means of the speaker 130 may be proportional to the velocity of the diaphragm, to the acceleration of the diaphragm or to the displacement of the diaphragm. FIGS. 2A-2C show characteristic of the systems that operate on a velocity signal, an acceleration signal and a displacement signal, respectively, where the frequency is plotted horizontally and the sound pressure level is plotted vertically.
As shown in FIG. 2A, in the velocity system, when the feedback gain xcex2 of the signal proportional to the velocity of the diaphragm (feedback rate D1) is increased, Q0 of the speaker system decreases and the sound pressure level in the vicinity of the lowest resonance frequency f0 is decreased. As shown in FIG. 2B, in the acceleration system, when the feedback gain of the signal proportional to the acceleration of the diaphragm (feedback rate D2) is increased, the sound pressure level is decreased and Q0 is increased, though the lowest resonance frequency f0 of the speaker system is decreased and sound reproduction in the bass region becomes possible.
As shown in FIG. 2C, in the displacement system, the lowest resonance frequency f0 is increased and Q0 of the speaker system is increased, when the feedback gain xcex2 of the signal proportional to the displacement of the diaphragm (feedback rate D3) is increased. For the reasons stated above, in the related-art MFB speaker system, an appropriate combination of the signals respectively proportional to the vibration velocity, vibrational acceleration and vibration displacement is often fed back.
Since the related-art MFB speaker system is constructed as described above, the amplifier 110, the speaker 130 and the feedback circuit 120 function as a single system as shown in FIG. 1. Therefore, a user of the speaker system cannot generally use an amplifier in his or her possession. When the amplifier 110 of the MFB speaker system is changed in an attempt to gain high performance, readjustment of the speaker 130 and the feedback circuit 120 is required. Thus, there was generally a problem in that a user cannot exchange an amplifier in the related-art MFB speaker system.
Accordingly, a general object of the present invention is to provide a MFB speaker system constructed such that a speaker unit having double voice coils is used, the amplifier in the speaker system is used only to amplify a signal from the speaker detected as a result of oscillation of the speaker, and an amplifier in the user""s possession or the user""s choice may be used as the unit-driving amplifier.
Another and more specific object of the present invention is to provide a MFB speaker system in which double voice-coil speaker unit, used conventionally for bass reproduction, is used, and in which an amplifier for amplifying oscillation information such as vibrational velocity, vibrational acceleration, and vibrational displacement is provided separately from an amplifier for driving the speaker unit with an acoustic signal, so that a user can use the amplifier in his or her possession or use an amplifier of his or her own choice.
The above objects can be achieved by a MFB speaker system comprising: a speaker unit provided with a first--voice coil for inputting an external acoustic signal and a second voice coil for inputting vibrational information obtained by outputting the acoustic signal; vibrational information detecting means for detecting the vibrational information of the speaker unit; and amplifying means for amplifying the vibrational information detected by the vibrational information detecting means and feeding back the vibrational information to the second voice coil with one of a positive and negative polarity with respect to the external acoustic signal.
The vibrational information of the speaker unit may be a signal proportional to a vibrational velocity of a diaphragm of the speaker unit.
The vibrational information of the speaker unit may be a signal proportional to a vibrational acceleration of a diaphragm of the speaker unit.
The vibrational information of the speaker unit may be a signal proportional to a vibrational displacement of a diaphragm of the speaker unit.
The amplifying means may at least include an amplifier for amplifying only the vibrational information of the speaker unit.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational displacement of a diaphragm of the speaker unit and a signal proportional to a vibrational velocity of the diaphragm.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational displacement of a diaphragm of the speaker unit and generate a signal proportional to a vibrational velocity of the diaphragm by differentiating the signal proportional to the vibrational displacement; and the amplifying means may amplify the signal proportional to the vibrational displacement and the signal proportional to the vibrational velocity and feed back the signals to the second voice coil.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational velocity of a diaphragm of the speaker unit and generate a signal proportional to a vibrational displacement of the diaphragm by integrating the signal proportional to the vibrational velocity; and the amplifying means may amplify the signal proportional to the vibrational displacement and the signal proportional to the vibrational velocity and feed back the signals to the second voice coil.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational displacement of a diaphragm of the speaker unit and a signal proportional to a vibrational acceleration of the diaphragm.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational displacement of a diaphragm of the speaker unit and generate a signal proportional to a vibrational acceleration of the diaphragm by differentiating the signal proportional to the vibrational displacement; and the amplifying means may amplify the signal proportional to the vibrational displacement and the signal proportional to the vibrational acceleration and feed back the signals to the second voice coil.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational acceleration of a diaphragm of the speaker unit and generate a signal proportional to a vibrational displacement of the diaphragm by integrating the signal proportional to the vibrational acceleration; and the amplifying means may amplify the signal proportional to the vibrational displacement and the signal proportional to the vibrational acceleration and feed back the signals to the second voice coil.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational velocity of a diaphragm of the speaker unit and a signal proportional to a vibrational acceleration of the diaphragm.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational velocity of a diaphragm of the speaker unit and generate a signal proportional to a vibrational acceleration of the diaphragm by differentiating the signal proportional to the vibrational velocity; and the amplifying means may amplify the signal proportional to the vibrational velocity and the signal proportional to the vibrational acceleration and feed back the signals to the second voice-coil.
The vibrational information detecting means may retrieve, as the vibrational information, a signal proportional to a vibrational acceleration of a diaphragm of the speaker unit and generate a signal proportional to a vibrational velocity of the diaphragm by integrating the signal proportional to the vibrational acceleration; and the amplifying means may amplify the signal proportional to the vibrational velocity and the signal proportional to the vibrational acceleration and feed back the signals to the second voice coil.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement, vibrational velocity and vibrational acceleration of a diaphragm of the speaker unit, so as to output a sum signal obtained by adding a signal indicating the vibrational displacement, a signal indicating the vibrational velocity and a signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement and vibrational acceleration of a diaphragm of the speaker unit and generate a signal indicating a vibrational velocity by differentiating a signal indicating the vibrational displacement so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, the signal indicating the vibrational velocity and a signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement and vibrational acceleration of a diaphragm of the speaker unit and generate a signal indicating a vibrational velocity by integrating a signal indicating the vibrational acceleration so as to output a sum signal obtained by adding the signal indicating a vibrational displacement, the signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement and vibrational velocity of a diaphragm of the speaker unit and generate a signal indicating a vibrational acceleration by differentiating a signal indicating the vibrational velocity so as to output a sum signal obtained by adding the signal indicating a vibrational displacement, the signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement and vibrational velocity of a diaphragm of the speaker unit and generate a signal indicating a vibrational acceleration by differentiating a signal indicating the vibrational displacement so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, a signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational velocity and vibrational acceleration of a diaphragm of the speaker unit and generate a signal indicating a vibrational displacement by integrating a signal indicating the vibrational velocity so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, the signal indicating the vibrational velocity and a signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational velocity and vibrational acceleration of a diaphragm of the speaker unit and generates a signal indicating a vibrational displacement by integrating a signal indicating the vibrational acceleration so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, a signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational displacement of a diaphragm of the speaker unit and generate a signal indicating a vibrational velocity and a signal indicating a vibrational acceleration by integrating a signal indicating the vibrational displacement so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, the signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational velocity of a diaphragm of the speaker unit, generate a signal indicating a vibrational displacement by integrating a signal indicating the vibrational velocity and generate a signal indicating a vibrational acceleration by differentiating a signal indicating the vibrational displacement so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, the signal indicating the vibrational velocity and the signal indicating the vibrational acceleration.
The vibrational information detecting means may detect, as the vibrational information, a vibrational acceleration of a diaphragm of the speaker unit and generate a signal indicating a vibrational displacement and a signal indicating a vibrational velocity by integrating a signal indicating the vibrational acceleration so as to output a sum signal obtained by adding the signal indicating the vibrational displacement, the signal indicating the vibrational velocity and a signal indicating the vibrational acceleration.
The vibration information detecting means may adjust the level of a signal indicating the vibrational displacement.
The vibration information detecting means may adjust the level of a signal indicating the vibrational velocity.
The vibration information detecting means may adjust the level of a signal indicating the vibrational acceleration.